Between 1977 and 2011, which national flag was unique with just one color and no design, insignia, or other details?

The flag of the Kingdom of Libya was adopted when Libya gained full independence in 1951. It consisted of a white star and crescent on a triband red-black-green design, with the central black band being twice the width of the outer bands. Following the coup d'état of 1969, the flag was replaced by the Pan-Arab red-white-black tricolor of the Arab Liberation Flag, first flown after the Egyptian Revolution of 1952 (which also formed the basis of the flags of Egypt, Iraq, Syria, and Yemen).

The flag of the Libyan Arab Jamahiriya was adopted on 11 November 1977 and consisted of a green field. It was the only national flag in the world with just one color and no design, insignia, or other details. It was chosen by Libyan leader Muammar Gaddafi.

During the Libyan Civil War against the rule of Muammar Gaddafi, the 1951–1969 flag – as well as various makeshift versions without the crescent and star symbol, or without the green stripe – came back into use in areas held by the Libyan opposition and by protesters at several Libyan diplomatic missions abroad. The National Transitional Council, formed on 27 February 2011, adopted the flag previously used in the Kingdom of Libya between 1951 and 1969 as the "emblem of the Libyan Republic".